Hyperthyroidism & Hind Limb Weakness in Cats

by Sarah Whitman

This is a microscopic image of the thyroid gland.

Hyperthyroidism affects your kitty's thyroid gland. It results in overproduction of the thyroid hormone, and causes a variety of symptoms, depending on the stage of illness. If it progresses too far, hyperthyroidism can affect the heart; this, in turn, can cause hind limb weakness and hind limb paralysis.

What Is Hyperthyroidism?

Hyperthyroidism is the medical term for an overactive thyroid gland, and it's one of the most commonly diagnosed hormonal disorders in cats. It can affect both males and females, and is most common in middle-aged and senior cats. Symptoms include weight loss, increased appetite, increased thirst and urination, restlessness, vomiting and diarrhea. Hyperthyroidism can also affect a cat's heart, which may in turn lead to other conditions that cause rear limb weakness. These conditions include thyrotoxic periodic paralysis and hypertrophic cardiomyopathy.

Thyrotoxic Periodic Paralysis

Thyrotoxic periodic paralysis is sometimes seen in cases of hyperthyroidism, and it causes episodes of muscle weakness, including limb weakness. Other symptoms can include difficulty breathing and swallowing. In humans, the weakness and paralysis in these episodes is more common in the legs rather than arms, suggesting a parallel to cats' hind limbs. Thyrotoxic periodic paralysis can be triggered by high-salt, high-carbohydrate foods, as well as other factors. Symptoms of thyrotoxic periodic paralysis subside between episodes.

Hypertrophic Cardiomyopathy in Cats

Hypertrophic cardiomyopathy can be another side effect of hyperthyroidism. It causes the heart muscle to thicken and become less efficient, causing problems throughout the body. If a cat reaches this stage of illness, chances of recovery decrease. In some cases of hypertrophic cardiomyopathy, a cat can experience sudden weakness and subsequent paralysis in his hind legs. This is due to the formation of blood clots which begin in the heart and travel to the hind limbs.

Diagnosis and Treatment

Because hyperthyroidism is common in cats, vets are more aware of diagnosis and treatment. With early diagnosis, treatment can be quite successful, and several options exist. These include putting a cat on medications, performing a thyroidectomy -- surgery to remove the abnormal thyroid lobe -- or performing radioactive iodine therapy. Take your kitty to the vet twice a year and ask for thyroid tests. This will help catch hyperthyroidism early, enhancing chances of successful treatment and avoiding reactions like rear limb weakness.

About the Author

Sarah Whitman's work has been featured in newspapers, magazines, websites and informational booklets. She is currently pursuing a master's degree in nutrition, and her projects feature nutrition and cooking, whole foods, supplements and organics. She also specializes in companion animal health, encouraging the use of whole foods, supplements and other holistic approaches to pet care.